This invention pertains to the field of microbial polysaccharides. In this field it is known that a common feature of certain microorganisms is the production of exocellular heteropolysaccharides. Heteropolysaccharides are high molecular weight generally linear carbohydrate polymers containing two or more kinds of monosaccharides that form a repeating unit that is polymerized.
Heteropolysaccharides are widely used in food, well drilling, agricultural and a wide variety of other industrial applications. Commercial demand for these water soluble gums has greatly increased over the last few decades. Furthermore, new industrial techniques create a need for heteropolysaccharides with new physical properties. Consequently, the need for heteropolysaccharides with different functionalities, coupled with commercial demand, has clearly indicated the necessity for the development of new heteropolysaccharides with new and different physical properties.
Acid stable heteropolysaccharides are of interest in oilfield applications, particularly in production enhancement operations. Enhancement of recovery of oil and gas from underground reservoirs can be accomplished by various stimulation techniques. One technique that has been widely employed is known as "acidizing". This technique comprises introducing an acid, preferrably a non-oxidizing acid, into the well under sufficient pressure to force the acid out into the underground formation where it reacts with the acid soluble components of the formation such as, for example, limestones, dolomites and sandstones containing streaks of carbonates. During acidizing, passageways for fluid flow within the formation are created or existing passageways are enlarged, thus increasing the porosity and permeability of the formation and, therefore, increasing oil and gas production from the underground reservoir.
The heteropolysaccharide produced by Xanthomonas campestris (xanthan gum) which contains glucose, mannose and glucuronic acid has found wide use in secondary oil recovery applications. In U.S. Pat. No. 3,236,305, a method of acidizing wells utilizing xanthan gum is shown. In U.S. Pat. No. 4,244,826, xanthan gum is also shown for use in gelled acidic well treating compositions.
Organisms classified as Agrobacterium radiobacter IFO (Institute of Fermentation, Osaka) 12607, IFO 12664, IFO 12665, IFO 13127, IFO 13256, IFO 13532 and IFO 13533 have been used to produce exocellular polysaccharides (Hiramatsu, et al., "Acidic Polysaccharides Containing Succinic Acid in Various Strains of Agrobacterium", Carbohydrate Research, (1978) 61, 96-98. These organisms were grown in a synthetic medium described in Amemura, et al., Hakko Kogaku Zasshi; (1971) 49, 559-564, Chem. Abst. 75, 1971, 74882j.
An exopolysaccharide containing D-glucose, D-galactose, pyruvic acid, and O-acetyl groups in the approximate proportions 6:1:1:1.5 is described by L. Zevenhuizen, "Methylation Analysis of Acidic Exopolysaccharides of Rhizobium and Agrobacterium", Carbohydrate Research, (1973) 26, 409-419. The organisms used by Zevenhuizen are described as Agrobacterium tumefaciens A-8 and A-10.
The organisms Agrobacterium radiobacter (IFO 12665) has been used to produce polysaccharides having a similar structure to that reported by Zevenhuizen (T. Harada, et al., "Comparative Studies of Polysaccharides Elaborated by Rhizobium, Alcaligenes, and Agrobacterium", Carbohydrate Research, (1979) 77, 285-288). Additionally, the polysaccharide isolated from a Pseudomonas organism reported in A. G. Williams, et al., "Preliminary Studies on the Composition and Rheological Properties of the Extracellular Polysaccharide Synthesized by Pseudomonas PBl (NCIB 11264)", Biochem. Biophys. Acta, 585 (4) 611-619 (1979) has a similar structure.
U.S. Pat. Nos. 4,259,451; 4,269,939 and 4,339,239 disclose a heteropolysaccharide for use in the control of color migration during dying of fabrics which has a composition similar to those described above.
It is an object of the present invention to provide an improved acid stable heteropolysaccharide which is produced by an unidentified Agrobacterium species. It is also an object of this invention to provide a heteropolysaccharide which thickens acid solutions, particularly hydrochloric acid solutions, containing high acid concentrations. It is an additional object of the present invention to provide an improved acidizing fluid composition with enhanced acid stability. It is still another object of this invention to provide a method for making this acid stable heteropolysaccharide. A still further object is to provide microorganisms for making the improved heteropolysaccharide. These and other objects of the invention will become apparent from the ensuing description.